Wear-resistant, superabrasive materials are traditionally utilized for a variety of mechanical applications. For example, polycrystalline diamond (“PCD”) materials are often used in drilling tools (e.g., cutting elements, gage trimmers, etc.), machining equipment, bearing apparatuses, wire-drawing machinery, and in other mechanical systems.
Conventional superabrasive materials have found utility as superabrasive cutting elements in rotary drill bits, such as roller cone drill bits and fixed-cutter drill bits. A conventional cutting element may include a superabrasive layer or table, such as a PCD table. The cutting element may be brazed, press-fit, or otherwise secured into a preformed pocket, socket, or other receiving space formed in the rotary drill bit. In another configuration, the substrate may be brazed or otherwise joined to an attachment member such as a stud or a cylindrical backing. Generally, a rotary drill bit may include one or more PCD cutting elements affixed to a bit body of the rotary drill bit.
As mentioned above, conventional superabrasive materials have found utility as bearing elements in thrust-bearing and radial bearing apparatuses. A conventional bearing element typically includes a superabrasive layer or table, such as a PCD table, bonded to a substrate. One or more bearing elements may be mounted to a bearing rotor or stator by press-fitting, brazing, mechanically coupled, or through other suitable methods of attachment. Typically, bearing elements mounted to a bearing rotor have superabrasive faces configured to contact corresponding superabrasive faces of bearing elements mounted to an adjacent bearing stator.
Cutting elements having a PCD table may be formed and bonded to a substrate using an ultra-high pressure, ultra-high temperature (“HPHT”) sintering process. Often, cutting elements having a PCD table are fabricated by placing a cemented carbide substrate, such as a cobalt-cemented tungsten carbide substrate, into a container or cartridge with a volume of diamond particles positioned on a surface of the cemented carbide substrate. A number of such cartridges may be loaded into an HPHT press. The substrates and diamond particle volumes may then be processed under HPHT conditions in the presence of a catalyst material that causes the diamond particles to bond to one another to form a diamond table having a matrix of bonded diamond crystals. The catalyst material is often a metal-solvent catalyst, such as cobalt, nickel, or iron, which facilitates intergrowth and bonding of the diamond crystals.
In one conventional approach, a constituent of the cemented-carbide substrate, such as cobalt from a cobalt-cemented tungsten carbide substrate, liquefies and sweeps from a region adjacent to the volume of diamond particles into interstitial regions between the diamond particles during the HPHT process. The cobalt may act as a catalyst to facilitate the formation of bonded diamond crystals. A metal-solvent catalyst may also be mixed with a volume of diamond particles prior to subjecting the diamond particles and substrate to the HPHT process.
The presence of the metal-solvent catalyst and/or other materials in the diamond table may reduce the thermal stability of the diamond table at elevated temperatures. For example, the difference in thermal expansion coefficient between the diamond grains and the metal-solvent catalyst is believed to lead to chipping or cracking in the PCD table of a cutting element during drilling or cutting operations. The chipping or cracking in the PCD table may degrade the mechanical properties of the cutting element or lead to failure of the cutting element. Additionally, at high temperatures, diamond grains may undergo a chemical breakdown or back-conversion with the metal-solvent catalyst. Further, portions of diamond grains may transform to carbon monoxide, carbon dioxide, graphite, or combinations thereof, thereby degrading the mechanical properties of the PCD material.
Accordingly, it is desirable to remove metal-solvent catalyst from a PCD material in situations when the PCD material may be exposed to high temperatures. Chemical leaching is often used to dissolve and remove various materials from the PCD layer. For example, chemical leaching may be used to remove metal-solvent catalysts, such as cobalt, from regions of a PCD layer that may experience elevated temperatures during drilling, such as regions adjacent to the working surfaces of the PCD layer.
Conventional chemical leaching techniques often involve the use of highly concentrated and corrosive solutions, such as highly acidic solutions, to dissolve and remove metal-solvent catalysts from polycrystalline diamond materials. However, in addition to dissolving metal-solvent catalysts from a PCD material, leaching solutions may also dissolve any accessible portions of a substrate to which the PCD material is attached. For example, highly acidic leaching solutions may dissolve any accessible portions of a cobalt-cemented tungsten carbide substrate, causing undesired pitting and/or other corrosion of the substrate surface.
In some conventional leaching techniques, a polymeric leaching cup may be placed around a portion of a PCD element to protect the substrate from a leaching solution. A polymeric leaching cup may, for example, surround the substrate surface and a portion of the PCD layer near the substrate. Such leaching cups may not, however, provide adequate protection under various leaching conditions. It may be desirable to expose PCD articles to leaching solutions for varying periods of time and/or to expose the PCD articles to leaching solutions under various temperature and/or pressure conditions to obtain specified leach depths. While various temperatures, pressures, and leach times may enable leaching of a PCD article to a desired degree, such conditions may undesirably cause portions of the substrate of the PCD article to be exposed to a leaching solution. For example, a leaching solution may pass between portions of the cup and the PCD article, resulting in portions of the substrate or other protected part of the PCD article being exposed to the leaching solution. Additionally, gases, such as air, may be trapped between a leaching cup and a PCD article when the cup is placed around the PCD article. During leaching, trapped gases may expand due to an increase in temperature and/or a decrease in pressure, pushing the PCD article out of the leaching cup and exposing a portion of the substrate or other protected part of the PCD article to the leaching solution. Such exposure to leaching solutions may result in undesired corrosion and/or damage to PCD substrates.
U.S. patent application Ser. No. 12/555,715 (now published as U.S. Patent Application Publication No. 2011/0056141) discloses other examples of processing superabrasive elements that include the use of protective layers formed on portions of the superabrasive elements. The disclosure of U.S. patent application Ser. No. 12/555,715 is incorporated herein, in its entirety, by this reference.